1. Field of the Invention
The present invention relates to a valve train mechanism of an internal combustion engine for opening or closing a valve (an intake valve, an exhaust valve) by swinging a rocker arm by rotation of a cam.
2. Related Art
Conventionally, there is known a structure, to lubricate a sliding contact portion between a rocker arm and a cam, which includes an oil injection hole formed at a bearing of the rocker arm through which lubricating oil in an oil passage in a rocker shaft is injected (see Patent Document 1: Japanese Utility Model Laid-Open Publication No. 59-116509).
However, according to the structure disclosed in the Patent Document 1, since the oil injection hole communicates with the oil passage in the rocker shaft at all times, the pressure of lubricating oil is difficult to control. Particularly, in a low-speed rotation range of an engine, the rotation speed of an oil pump is low, and hence, the lubricating oil pressure becomes low, and when the lubricating oil is continuously injected from the oil injection hole of the rocker arm, the oil pressure may become insufficient, which provides a fear of preventing desirable supply of the lubricating oil to respective components or portions of the engine.